In recent years there has been growing interest in organic electronic (OE) devices, for example organic field effect transistors (OFET) for use in backplanes of display devices or logic capable circuits, and organic photovoltaic (OPV) devices. A conventional bottom gate OFET comprises a gate electrode, a gate insulator layer made of a dielectric material (also referred to as “dielectric” or “gate dielectric”), source and drain electrodes, a semiconducting layer made of an organic semiconductor (OSC) material, and typically a passivation layer on top of the OSC layer to protect it against environmental influence and/or damage from subsequent device manufacturing steps.
For OFET devices in particular solution processable passivation layers are desired. The key requirements for materials used in such passivation layers are orthogonality of the passivation layer solvent with the OSC layer, and adhesion to the underlying layers. The passivation materials should be solution based and should be suitable for solution based deposition methods like spin-coating, or wider area printing methods including flexo, gravure and slot-die coating.
One aim of the present invention is to provide passivation layers and materials used therein which meet these requirements. Another aim is to provide improved methods of manufacturing such passivation layers. Another aim is to provide improved OE devices, in particular OFETs, more specifically bottom gate OFETs, comprising such passivation layers. Further aims are immediately evident to the person skilled in the art from the following description.
The inventors have found these aims can be achieved by providing passivation layers for use in OFET devices, methods of manufacturing such passivation layers, and passivation materials comprised therein, in accordance with the present invention and as claimed hereinafter. In particular, it was found that the above aims could be achieved by using a three layer passivation stack, comprising                a bottom layer that is deposited on the OSC layer and contains a material having good adhesion to the OSC layer and being processable from solvents that are orthogonal to the OSC layer,        a top layer that provides good resistance to subsequent device manufacturing steps, and        an intermediate layer that is provided between the bottom layer and the top layer and provides good adhesion between the bottom and the top layer, and preferably also good solvent resistance to prevent that the bottom layer swells in the solvent used for the top layer.        
Such a passivation layer stack was found to provide adequate adhesion to the OSC and between the individual passivation layers, to provide a top surface that is resistant to subsequent device manufacturing steps, especially to metal deposition and etching processes, and to be especially suitable for mass production of OFET devices. The bottom layer of the passivation layer stack can also be deposited onto a patterned OSC layer which is provided on an organic gate dielectric layer, so that the adhesion of the bottom layer to both the OSC and the underlying organic gate dielectric should be strong.